(a) A gene is a unit of inheritance that is transferred from the parent to the offspring. It controls the expression of a character. The gene which can express its character even when it is present as a single copy is called a dominant gene. Also it is able to express its characters in all the generations.
However, a gene which can express its character, only when it is present in pairs is called a recessive gene.
(b) (i) BB - brown eyes
(ii) bb - blue eyes
(iii) Bb - brow eyes